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The stratigraphy of the latest Triassic through to the earliest Cretaceous of the Portland-Wight Basin and its adjacent areas may be subdivided using petrophysical (gamma-ray and interval transit time) criteria, in association with gross lithology to allow a total of 50 lithological units to be recognized. Three units occur within the latest Triassic, 46 in the Jurassic and one in the earliest Cretaceous. The lithostratigraphy can be integrated into a biostratigraphic template using published data and subsequent observations based on micropalaeontology (ostracods, foraminiferids) and palynology (dinocysts, miospores). Throughout the study area recognition of major lithostratigraphic and biostratigraphic events enables the chronostratigraphic framework of the basin to be determined, which has aided identification of regional stratigraphic breaks throughout much of the Portland-Wight Basin, including haitii in proximity to the Pliensbachian-Toarcian and the Aalenian-Bajocian boundaries, and also within the Late Oxfordian. Although the majority of the lithostratigraphic events have been deduced to be isochronous, a number of lithological units exhibit significant diachroneity.

Three detailed biostratigraphic zonations, based on ostracods, foraminiferids and dinocysts, are proposed for the latest Triassic through to the earliest Cretaceous of the Portland-Wight Basin and its adjacent areas. A total of 112 zones-zonules (34 ostracod zones/subzones, 25 foraminiferid zones, 53 dinoflagellate zones, subzones and zonules) are recognized. All three zonation schemes are based on samples obtained from both outcrop (the Dorset coast) and boreholes, the latter from ditch cuttings, with some conventional and sidewall core samples, in association with published data, and have where possible been calibrated to the standard ammonite zones recognized throughout northwest Europe.Notable occurrences include Pseudomacrocypris subtriangularis and Cardobairdia sp. B sensu Ainsworth.Age: latest Rhaetian-Early Sinemurian (pre planorbis-bucklandi ammonite zones). Occurring within the Blue Lias.

A new foraminiferal species, Saracenella mochrasensis, reported previously under the name of Saracenelln sp. A, is formally described and figured and its stratigraphic distribution precisely established. The distinct morphology and short stratigraphic range of this species within the Toarcian (Lower Jurassic) of the Mochras Borehole and of the Iberian Range, Northwest and Southwest Europe respectively, make it an excellent biostratigraphic marker species for the uppermost Toarcian, Moorei-Aalensis Subzones (Levesquei Zone) in Northwest Europe and Mactra Subzone (Aalensis Zone) in Southwest Europe.